Synchronization timing detector, wireless communication device, and non-transitory computer-readable recording medium

ABSTRACT

A synchronization timing detector includes n correlators, a calculation unit, and a symbol timing estimating unit. The n correlators calculate and output correlation values, between a received signal oversampled m times for one symbol period and a known synchronization pattern, by shifting sample timings by m/n samples each, where m is a natural number, and n is a natural number that satisfies 3≤n≤m and is a divisor of m. The calculation unit generates n correlation value vectors by arranging the correlation values output from the n correlators on polar coordinates at intervals of an angle of 2π(n/m) radians, and adds the n correlation value vectors to calculate an angle of a resultant vector of the correlation value vectors. The symbol timing estimating unit estimates a symbol timing of the received signal based on the angle of the resultant vector calculated by the calculation unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of PCT International Application No.PCT/JP2019/048446 filed on Dec. 11, 2019 which claims the benefit ofpriority from Japanese Patent Application No. 2019-049897 filed on Mar.18, 2019, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a synchronization timing detector, awireless communication device, and a non-transitory computer-readablerecording medium.

2. Description of the Related Art

In digital wireless communications, the transmitter side transmits dataon a frame-by-frame basis in which a synchronization word having acertain signal sequence pattern is arranged. The receiver side detectsthe synchronization word, thereby carrying out symbol synchronization todemodulate received data.

For example, Japanese Patent No. 5,283,182 discloses a technique that,even when received power substantially fluctuates, enablessynchronization with symbols in a received signal.

However, conventionally, when detecting symbol synchronization, acorrelation value with a synchronization word is calculated for eachsample at a sampling rate that is more than ten times (for example, 16times) as high as a symbol rate. As a result, the amount of informationprocessing increases, and the processing load for detecting symbolsynchronization increases.

SUMMARY OF THE INVENTION

A synchronization timing detector according the present disclosureincludes n correlators, a calculation unit, and a symbol timingestimating unit. The n correlators are configured to calculate andoutput correlation values, between a received signal oversampled m timesfor one symbol period and a known synchronization pattern, by shiftingsample timings by m/n samples each, where m is a natural number, and nis a natural number that satisfies 3≤n≤m and is a divisor of m. Thecalculation unit is configured to generate n correlation value vectorsby arranging the correlation values output from the n correlators onpolar coordinates at intervals of an angle of 2π(n/m) radians, and addthe n correlation value vectors to calculate an angle of a resultantvector of the correlation value vectors. The symbol timing estimatingunit is configured to estimate a symbol timing of the received signalbased on the angle of the resultant vector calculated by the calculationunit.

A wireless communication device according to the present disclosureincludes a detection unit configured to detect a radio frequency signaland convert the radio frequency signal into a received signal; ademodulation unit configured to demodulate the received signal; and asynchronization timing detector configured to generate a synchronizationsignal used by the demodulation unit for demodulating the receivedsignal. The synchronization timing detector includes n correlators, acalculation unit, a symbol timing estimating unit, and synchronizationsignal generating unit. The n correlators are configured to calculateand output correlation values, between the received signal oversampled mtimes for one symbol period and a known synchronization pattern, byshifting sample timings by m/n samples each, where m is a naturalnumber, and n is a natural number that satisfies 3≤n≤m and is a divisorof m. The calculation unit is configured to generate n correlation valuevectors by arranging the correlation values output from the ncorrelators on polar coordinates at intervals of an angle of 2π(n/m)radians, and add the n correlation value vectors to calculate an angleof a resultant vector of the correlation value vectors. The symboltiming estimating unit is configured to estimate a symbol timing of thereceived signal based on the angle of the resultant vector calculated bythe calculation unit. The synchronization signal generating unit isconfigured to generate the synchronization signal based on the estimatedsymbol timing.

A non-transitory computer-readable recording medium according to thepresent disclosure contains a computer program. The computer programcauses a computer to execute calculating and outputting n correlationvalues, between a received signal oversampled m times for one symbolperiod and a known synchronization pattern, by shifting sample timingsby m/n samples each, where m is a natural number, and n is a naturalnumber that satisfies 3≤n≤m and is a divisor of m; generating ncorrelation value vectors by arranging the n correlation values on polarcoordinates at intervals of an angle of 2π(n/m) radians, and adding then correlation value vectors to calculate an angle of a resultant vectorof the n correlation value vectors; and estimating a symbol timing ofthe received signal based on the angle of the resultant vector.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of the configurationof a wireless communication device according to an embodiment of thepresent disclosure;

FIG. 2 is a block diagram illustrating an example of the configurationof a synchronization timing detector according to the embodiment of thepresent disclosure;

FIG. 3 is a schematic diagram illustrating correlation values of samplesin one period in the present embodiment;

FIG. 4 is a schematic diagram for explaining an example of a method ofarranging the correlation values on polar coordinates;

FIG. 5 is a schematic diagram for explaining an example of a method ofcalculating the correlation values in the form of correlation valuevectors;

FIG. 6 is a schematic diagram for explaining x components and ycomponents of the correlation values;

FIG. 7 is a functional block diagram illustrating in detail thesynchronization timing detector according to the embodiment of thepresent disclosure;

FIG. 8 is a schematic diagram illustrating a correlation value vectorcorresponding to a prediction angle; and

FIG. 9 is a flowchart illustrating an example of a process flow fordetecting a synchronization timing according to the present embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment according to the present disclosure will be described indetail with reference to the accompanying drawings. The presentdisclosure is not limited by this embodiment and, when there are aplurality of embodiments, includes combinations of at least some of suchembodiments.

EMBODIMENT

The configuration of a wireless communication device 1 according to theembodiment of the present disclosure will be described with reference toFIG. 1. FIG. 1 is a block diagram illustrating an example of theconfiguration of the wireless communication device 1.

The wireless communication device 1 includes an antenna 10, a detectionunit 20, a synchronization timing detector 30, a demodulation unit 40,and a control unit 50. In the present embodiment, the wirelesscommunication device 1 is a digital wireless communication device.

The antenna 10 receives a radio frequency (RF) signal transmitted from awireless communication device different from the wireless communicationdevice 1. The antenna 10 receives, for example, an RF signal modulatedby a 4-value frequency shift keying (FSK). The antenna 10 outputs thereceived RF signal to the detection unit 20.

The detection unit 20 detects the RF signal. Specifically, the detectionunit 20 includes, for example, an RF circuit unit, an orthogonaldetection unit, an analog-to-digital (A/D) conversion unit, and areceived-data converting unit, which are not illustrated. The RF circuitunit executes processing for changing the frequency of the RF signalreceived from the antenna 10. The RF circuit unit, for example, changesthe signal into an intermediate frequency and outputs the resultantsignal to the orthogonal detection unit. The orthogonal detection unitexecutes orthogonal detection on the signal received from the RF circuitunit and outputs the detected orthogonal signals to the A/D conversionunit. The A/D conversion unit executes analog-to-digital conversion ontwo orthogonal signals I and Q obtained by orthogonal detection by theorthogonal detection unit, thereby converting these signals into digitalsignals, and outputs the resultant signals to the received-dataconverting unit. The received-data converting unit converts orthogonalsignals into a received signal. With respect to any signal that has beenmodulated by the aforementioned 4-value FSK, the received-dataconverting unit executes frequency modulation (FM) detection byarctangent detection on the signal to convert the signal into a receivedsignal. The received signal output from the received-data convertingunit is output to the synchronization timing detector 30 and thedemodulation unit 40.

The A/D conversion unit oversamples a signal, for example, more than tentimes (for example, 16 times) as high as a symbol rate. Therefore, areceived signal output from the received-data converting unit is asignal oversampled with respect to the symbol rate. Thus, the detectionunit 20 receives an RF signal and outputs a received signal that havebeen oversampled with respect to a symbol rate.

The synchronization timing detector 30 detects the timing of symbolsynchronization. The synchronization timing detector 30 outputs timinginformation (a symbol synchronization signal) regarding the timing forstarting the symbol synchronization. The synchronization timing detector30 also detects the timing for frame synchronization. Thesynchronization timing detector 30 outputs timing information (a framesynchronization signal) regarding the timing for starting the framesynchronization. The configuration of and processing to be performed bythe synchronization timing detector 30 will be described later.

The demodulation unit 40 executes demodulation processing on thereceived signal based on the timing information detected by thesynchronization timing detector 30.

The control unit 50 controls the units included in the wirelesscommunication device 1. That is, the control unit 50 controls thedetection unit 20, the synchronization timing detector 30, and thedemodulation unit 40. The control unit 50 is composed of, for example, acentral processing unit (CPU), a random access memory (RAM), a read onlymemory (ROM), and the like. In this case, the ROM stores thereincomputer programs that the CPU uses to control the units. The CPUcontrols the units in the wireless communication device 1 by reading outthe computer programs stored in the ROM and allocating data areas in theRAM to execute the computer programs. In other words, the control unit50 implements functions of the wireless communication device 1 accordingto the present embodiment by executing the computer programs recorded ina non-transitory computer-readable recording medium.

Synchronization Timing Detector

The synchronization timing detector according to the embodiment of thepresent disclosure will be described with reference to FIG. 2. FIG. 2 isa block diagram illustrating an example of the basic configuration ofthe synchronization timing detector according to the embodiment of thepresent disclosure.

The synchronization timing detector 30 includes a first correlator 31-1,a second correlator 31-2, . . . , an nth (n is a natural number of 3 orlarger) correlator 31-n, a calculation unit 32, and a symbol timingestimating unit 33.

Each of the first correlator 31-1 to the nth correlator 31-n receives areceived signal oversampled m times. The first correlator 31-1 to thenth correlator 31-n calculate correlation values R between signalsamples sampled at certain different sample timings and a knownsynchronization pattern. The certain sample timings are shifted by m/nsamples each. Here, n is a natural number that satisfies 3≤n≤m and is adivisor of m. For example, when m is 16 and n is 4, the sample timingsfor correlation values Rn are shifted by 4 samples each. The correlators31-1 to 31-4 calculate correlation values R1 to R4, respectivelystarting from the first, fifth, ninth, and thirteenth samples of 16samples (first to 16th samples) in one symbol period. That is, the firstcorrelator 31-1 calculates the correlation value R1 in one symbol periodfrom the first sample to the next first sample. The second correlator31-2 calculates a correlation value R2 in one symbol period from thefifth sample to the next fifth sample. The third correlator 31-3calculates a correlation value R3 in one symbol period from the ninthsample to the next ninth sample. The fourth correlator 31-4 calculates acorrelation value R4 in one symbol period from the thirteenth sample tothe next thirteenth sample. Thus, the four correlators 31-n calculatethe correlation values Rn with respect to the signal samples of thereceived signal, by shifting sample timings by 4 samples each. Each ofthe correlators calculates the corresponding correlation value based onExpression (1) given below.

$\begin{matrix}{{{Correlation}\mspace{14mu}{value}} = {\sum\limits_{k = 1}^{1}{{S\lbrack k\rbrack}*{B\lbrack k\rbrack}}}} & (1)\end{matrix}$

In Expression (1), S[k] is data of a synchronization word, and B[k] isreceived data that has been buffered. In addition, l (lower-case L) isthe data length of the synchronization word.

FIG. 3 illustrates a state in which the correlation values Rn outputfrom the n correlators, which are the first correlator 31-1 to nthcorrelator 31-n, are plotted for sample timings P1 to Pm. For example,the output of the first correlator 31-1 is illustrated with themagnitude of the corresponding correlation value indicated as an upwardarrow at the position of P1. The same applies to each of the secondcorrelator 31-2 to fourth correlator.

The calculation unit 32 repeats calculating the correlation values Rnuntil any one of the correlation values Rn exceeds a predeterminedthreshold. When any one of the correlation values Rn exceeds thepredetermined threshold, the calculation unit 32 arranges thecorrelation values Rn illustrated in FIG. 3 on polar coordinatesillustrated in FIG. 4. As a result, the correlation values Rn areexpressed on the polar coordinates as n correlation value vectors V1,V5, V9, and V13 whose magnitudes are the absolute values of thecorresponding correlation values and which are arranged at intervals ofan angle of 2π(n/m) radians, as illustrated in FIG. 5. The calculationunit 32 performs addition of the correlation value vectors V1, V5, V9,and V13. The calculation unit 32 calculates the angle of the resultantvector of the correlation value vectors on the polar coordinates. Forthe sake of simplifying description, the angle corresponding to thesample timing P1 is set to 0 radians.

The angle of the resultant vector of the correlation value vectors maybe calculated in such a manner that: the x component and the y componentof each of the correlation value vectors are calculated; the differenceamong the x components and the difference among the y components arecalculated; and an arctangent is calculated based on the calculated xcomponent and y component. For example, the calculation unit 32calculates the difference among the x components and the differenceamong the y components of the correlation value vectors V1, V5, V9, andV12 that are arranged at intervals of 90 degrees, where the number n ofcorrelators is 4. The calculation unit 32 calculates the x component andthe y component of each of the correlation value vectors usingExpression (2) below for the x component and using Expression (3) belowfor the y component, and then calculates the difference (Vx) among the xcomponents and the difference (Vy) among the y components as illustratedin FIG. 6.

$\begin{matrix}{{x\mspace{14mu}{component}} = {\sum\limits^{n}{{Correlation}\mspace{14mu}{value}\mspace{14mu}{for}\mspace{14mu}{nth}\mspace{14mu}{buffer}*\left( {{Angle}\mspace{14mu}{for}\mspace{14mu}{nth}\mspace{14mu}{buffer}} \right)}}} & (2) \\{{y\mspace{14mu}{component}} = {\sum\limits^{n}{{Correlation}\mspace{14mu}{value}\mspace{14mu}{for}\mspace{14mu}{nth}\mspace{14mu}{buffer}*\left( {{Angle}\mspace{14mu}{for}\mspace{14mu}{nth}\mspace{14mu}{buffer}} \right)}}} & (3)\end{matrix}$

The calculation unit 32 calculates an arctangent from the difference Vxand the difference Vy according to Expression (4) in order to obtain anangle of the resultant vector of the correlation value vectors on thepolar coordinates.

$\begin{matrix}{{Angle} = {\arctan\left( \frac{y\mspace{14mu}{component}\mspace{14mu}{of}\mspace{14mu}{correlation}\mspace{14mu}{value}}{x\mspace{14mu}{component}\mspace{14mu}{of}\mspace{14mu}{correltion}\mspace{14mu}{value}} \right)}} & (4)\end{matrix}$

The reason for the calculation unit 32 to perform addition of vectorsand obtain the angle is to estimate the sample timing at which acorrelation value becomes maximum. As illustrated in FIG. 3, thesynchronization timing detector 30 according to the embodiment of thepresent disclosure does not calculates the correlation valuescorresponding to all the sample timings P1 to P16 in one symbol period,but calculates the correlation values corresponding to only the sampletimings P1, P5, P9, P13 that are thinned out at the certain intervals.Therefore, it is needed to estimate the magnitude of the correlationvalue and the sample timing when the correlation value is maximized.

The calculation unit 32 arranges, on the polar coordinates, thecorrelation values corresponding to the sample timings that are thinnedout to obtain the correlation value vectors. Angles on the polarcoordinates can express 16 samples in one round, and angles formed bythe correlation value vectors indicate the sample timings that are thestarting points for calculating the correlation values. Therefore, theresultant vector of the correlation value vectors calculated by thecalculation unit 32 indicates a correlation value vector when thecorrelation value is maximized. Thus, an angle (prediction angle θ1)formed by the resultant vector of the correlation value vectorscalculated by the calculation unit 32 can be estimated to be a sampletiming at which a correlation value becomes maximum.

Based on the prediction angle θ1, the symbol timing estimating unit 33estimates a symbol timing at which a timing of a symbol included in thereceived signal and a timing of detecting the symbol of the receivedsignal at the receiver side are synchronized. As illustrated in FIG. 4,one round on the polar coordinates indicates one symbol period. Thesymbol timing estimating unit 33 estimates that the correlation valuebecomes maximum at the prediction angle θ1. The symbol timing estimatingunit 33 further estimates a sample timing that corresponds to the angleat which the correlation value becomes maximum because one round on thepolar coordinates indicates one symbol period, as illustrated in FIG. 4.The symbol timing estimating unit 33 further estimates the symbol timingfrom the sample timing at which the correlation value becomes maximum.Thus, when a received signal is sampled from the sample timing thatcorrespond to the prediction angle θ1, it can be said that thecorrelation value with the synchronization word becomes maximum. Becausethe correlation value with the synchronization word is maximized, it canbe said that estimation of the timing of the synchronization word hasbeen enabled. In addition, because the position (symbol timing) of asymbol in the waveform of the synchronization word is known, the sampletiming at which the correlation value with the synchronization wordbecomes maximum can be estimated, thereby enabling estimation of thetiming of the synchronization word itself and further enablingestimation of the symbol timing at which a timing of a symbol includedin the received signal and a timing of detecting the symbol of thereceived signal at the receiver side are synchronized.

Synchronization Timing Detecting Method

A synchronization timing detecting method in a wireless communicationdevice that includes a synchronization timing detector according to thepresent embodiment will be described with reference to FIG. 7. FIG. 7 isa functional block diagram illustrating in detail a synchronizationtiming detector according to the present embodiment.

In a synchronization timing detector 30A according to the presentembodiment, a sampling rate at the receiver side is set to m times ashigh as a sampling rate at the transmitter side, that is, for example,16-time oversampling is performed. In this case, the synchronizationtiming detector 30A includes 16 buffers. In the following description, acase where oversampling in which a sampling rate at the receiver side isset to 16 times as high as that at the transmitter side will bedescribed. However, this is merely an example and is not intended tolimit the present disclosure. For example, setting a sampling rate atthe receiver side may be set to more than ten times as high as asampling rate at the transmitter side.

The synchronization timing detector 30A according to the presentembodiment includes a first buffer 110-1 to a 16th buffer 110-16, thefirst correlator 31-1 to the fourth correlator 31-4, the calculationunit 32, the symbol timing estimating unit 33, a selector 34, asynchronization determination correlator 35, a frame timing determiningunit 36, and a symbol timing determining unit 37.

The 16 buffers each store therein a received signal by shifting storagetimings by one sample each. In the same manner as performed with thebasic configuration described using FIG. 2, the n correlators determinecorrelations between a synchronization word and individual signalsamples of a received signals output from the buffers corresponding tothe sample timings shifted by m/n samples. Here, n is a natural numberthat satisfies 3≤n≤m and is a divisor of m. Because the number ofcorrelators is 4, n equals 4. This means that the n correlatorscalculate correlation values between the synchronization word andindividual pieces of output from the buffers corresponding to the sampletimings shifted by 4 samples. The first correlator 31-1 calculates acorrelation value with respect to the output from the first buffer110-1; the second correlator 31-2 calculates a correlation value withrespect to the output from the fifth buffer 110-5; the third correlator31-3 calculates a correlation value with respect to the output from theninth buffer 110-9; and the fourth correlator 31-4 calculates acorrelation value with respect to the output from the thirteenth buffer110-13. The calculation unit 32 calculates the prediction angle θ1 inthe same manner as with the basic configuration illustrated in FIG. 2.Therefore, the description thereof is omitted.

Based on the prediction angle θ1 calculated by the calculation unit 32,the symbol timing estimating unit 33 estimates an applicable sampletiming from the sample timings Pm (P1 to P16) on the polar coordinatesillustrated in FIG. 4. Because one symbol period of the sample timingsPm corresponds to one round, the angle indicated by the prediction angleθ1 means a sample timing. In the strict sense, the prediction angle θ1at which the correlation value becomes maximum is not applicable to anyof the angles obtained by dividing one round into the equal 16 parts.Therefore, the symbol timing estimating unit 33 may estimate any one ofthe sample timings Pm that corresponds to the closest angle to theprediction angle θ1.

The symbol timing estimating unit 33 instructs the selector 34 toselect, based on the estimated value of the symbol timings Pm estimatedby the symbol timing estimating unit 33, the received signal stored inthe buffer that corresponds to the applicable sample timing.

For example, in the state illustrated in FIG. 3, FIG. 5, FIG. 6, andFIG. 8, the calculation unit 32 calculates the prediction angle θ1 asbeing 45 degrees. Based on 45 degrees given as the calculation result bythe calculation unit 32, the symbol timing estimating unit 33 estimatesthat the correlation value becomes maximum at the sample timing P3.Based on the estimation by the symbol timing estimating unit 33 that thecorrelation value becomes maximum at the sample timing P3, the selector34 selects the received signal stored in the third buffer 110-3 andoutputs the selected received signal to the synchronizationdetermination correlator 35.

The synchronization determination correlator 35 calculates a correlationvalue between the synchronization word and the received signal that isstored in the buffer corresponding to the timing P3, which is estimated,by the symbol timing estimating unit 33, to provide the maximumcorrelation value. The synchronization determination correlator 35 thenoutputs the calculated correlation value to the frame timing determiningunit 36 and the symbol timing determining unit 37.

When the correlation value calculated by the synchronizationdetermination correlator 35 is equal to or more than a certainthreshold, the frame timing determining unit 36 determines a frametiming. The frame timing determining unit 36 generates a framesynchronization signal based on the determined frame timing and outputsthe frame synchronization signal to the demodulation unit 40.

When the correlation value calculated by the synchronizationdetermination correlator 35 is equal to or more than a certainthreshold, the symbol timing determining unit 37 determines a symboltiming in the received signal. The symbol timing determining unit 37generates a symbol synchronization signal based on the determined symboltiming and outputs the symbol synchronization signal to the demodulationunit 40. The frame timing determining unit 36 and the symbol timingdetermining unit 37 both not only make the determinations but alsogenerate the respective synchronization signals. Therefore, these twounits are collectively referred to as a synchronization signalgenerating unit 38.

As described earlier, the demodulation unit 40 executes demodulationprocessing on the received signal based on the timing information, thatis, the frame synchronization signal and the symbol synchronizationsignal, detected by the synchronization timing detector 30.

According to the present embodiment, a symbol timing is estimated bycalculating correlation values for five buffers of the 16 buffers andcalculating an arctangent for predicting the maximum correlation value.The processing amount for calculating an arctangent, for example, whenthe calculation is replaced by a Chebyshev approximation formula, is thesame as in a case where a correlation value for one buffer iscalculated. That is, according to the present embodiment, when thesynchronization timing detector includes 16 buffers, a synchronizationtiming can be detected by the processing whose calculation amount is thesame as in the processing for calculating correlation values for 6buffers.

In contrast, according to the conventional method, when thesynchronization timing detector includes 16 buffers, correlation valuesfor all of the 16 buffers needs to be calculated in order to detect asynchronization timing, as described above. That is, the presentembodiment enables a detection of a synchronization timing with half orless calculation amount compared with the conventional method.

In the above description, the calculation unit 32 estimates a symboltiming by detecting correlation values for four buffers: the firstbuffer 110-1, the fifth buffer 110-5, the ninth buffer 110-9, and thethirteenth buffer 110-13. However, in the present disclosure, thecalculation unit 32 can estimate a symbol timing by calculating anglesthrough addition of vectors when there are 3 or more buffers.

The process flow for detecting a synchronization timing according to thepresent embodiment will be described with reference to FIG. 9. FIG. 9 isa flowchart illustrating an example of the process flow for detecting asynchronization timing according to the present embodiment.

A certain number of correlators (the first to the nth correlators) eachcalculate a correlation value between a received signal stored in thecorresponding buffer (certain buffer) and a synchronization word (StepS101).

When any of the correlation values calculated at Step S101 is equal toor more than a predetermined threshold (Yes at Step S102), thecalculation unit 32 calculates a prediction angle θ1 that corresponds tothe maximum correlation value on polar coordinates, based on thecorrelation values received from the correlators (Step S103).

When all the correlation values calculated at Step S101 are less thanthe certain threshold (No at Step S102), the flow returns to Step S101,and the calculation unit 32 calculates correlation values for thecertain buffers. This is processing for not performing processing atStep S103 and subsequence steps because none of the correlators outputlarge correlation values when a received signal is not a synchronizationword.

The symbol timing estimating unit 33 selects the buffer that correspondsto the sample timing that corresponds to the prediction angle θ1calculated by the calculation unit 32, and the synchronizationdetermination correlator 35 calculates a correlation value between thereceived signal stored in the selected buffer and the synchronizationword (Step S104).

When the correlation value calculated at Step S104 is less than apredetermined threshold (No at Step S105), the flow returns to StepS101.

When the correlation value calculated at Step S104 is equal to or morethan the predetermined threshold (Yes at Step S105), the frame timingdetermining unit 36 determines a frame timing and generates a framesynchronization signal, and the symbol timing determining unit 37determines a symbol timing and generates a symbol synchronization signal(Step S106). Thereafter, the processing in FIG. 9 ends.

The threshold on correlation values that is used for estimating a sampletiming at Step S102 may be lower than the threshold for a correlationvalue that is used by the synchronization determination correlator forsynchronization determination at Step S105. This is because, in thestage of the estimation, the phase of the received signal stored in thebuffers corresponding to the thinned-out sample timings (i.e., thestarting points for calculating the correlation values) is notnecessarily the same as the phase of the synchronization word, andtherefore, the correlation values do not tend to be large. In contrast,the synchronization determination correlator receives a received signalstored in the buffer corresponding to a sample timing estimated toprovide the maximum correlation value. It is therefore expected that thecorrelation value will be large, thus the threshold on the correlationvalue may be set to be large.

As described above, according to the present embodiment, when thereceiver side uses a sampling rate that is more than ten times higher,all of the buffers need to be used for calculating correlation values.Thus, the present embodiment suppresses the calculation amount fordetecting a synchronization timing to half or less than the calculationamount in the conventional method.

In addition, according to the present embodiment, a correlation valuefor the buffer predicted to correspond to a synchronization timing canbe calculated, and the correlation value thus calculated can be comparedwith correlation values for the buffers calculated for predicting asynchronization timing. As a result, the present embodiment enhancesdetection accuracy for a synchronization timing.

According to the present disclosure, the processing load for detecting asymbol synchronization can be reduced.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A synchronization timing detector comprising: ncorrelators configured to calculate and output correlation values,between a received signal oversampled m times for one symbol period anda known synchronization pattern, by shifting sample timings by m/nsamples each, where m is a natural number, and n is a natural numberthat satisfies 3≤n≤m and is a divisor of m; a calculation unitconfigured to generate n correlation value vectors by arranging thecorrelation values output from the n correlators on polar coordinates atintervals of an angle of 2π(n/m) radians, and add the n correlationvalue vectors to calculate an angle of a resultant vector of thecorrelation value vectors; and a symbol timing estimating unitconfigured to estimate a symbol timing of the received signal based onthe angle of the resultant vector calculated by the calculation unit. 2.A wireless communication device comprising: a detection unit configuredto detect a radio frequency signal and convert the radio frequencysignal into a received signal; a demodulation unit configured todemodulate the received signal; and a synchronization timing detectorconfigured to generate a synchronization signal used by the demodulationunit for demodulating the received signal, wherein the synchronizationtiming detector comprises: n correlators configured to calculate andoutput correlation values, between the received signal oversampled mtimes for one symbol period and a known synchronization pattern, byshifting sample timings by m/n samples each, where m is a naturalnumber, and n is a natural number that satisfies 3≤n≤m and is a divisorof m; a calculation unit configured to generate n correlation valuevectors by arranging the correlation values output from the ncorrelators on polar coordinates at intervals of an angle of 2π(n/m)radians, and add the n correlation value vectors to calculate an angleof a resultant vector of the correlation value vectors; and a symboltiming estimating unit configured to estimate a symbol timing of thereceived signal based on the angle of the resultant vector calculated bythe calculation unit; and a synchronization signal generating unitconfigured to generate the synchronization signal based on the estimatedsymbol timing.
 3. The wireless communication device according to claim2, wherein the synchronization timing detector comprises: m buffersconfigured to each store therein the received signal oversampled m timesfor one symbol period, by shifting storage timings by one sample each,where m is a natural number; a selector configured to select one bufferfrom the m buffers based on the symbol timing estimated by the symboltiming estimating unit; a synchronization determination correlatorconfigured to calculate a correlation value between the received signalstored in the buffer selected by the selector and a knownsynchronization pattern; a frame timing determining unit configured togenerate a frame synchronization signal as the synchronization signaland output the frame synchronization signal to the demodulation unitwhen the correlation value calculated by the synchronizationdetermination correlator is equal to or more than a certain threshold;and a symbol timing determining unit configured to generate a symbolsynchronization signal as the synchronization signal and output thesymbol synchronization signal to the demodulation unit when thecorrelation value calculated by the synchronization determinationcorrelator is equal to or more than a certain threshold.
 4. Anon-transitory computer-readable recording medium containing a computerprogram, the computer program causing a computer to execute: calculatingand outputting n correlation values, between a received signaloversampled m times for one symbol period and a known synchronizationpattern, by shifting sample timings by m/n samples each, where m is anatural number, and n is a natural number that satisfies 3≤n≤m and is adivisor of m; generating n correlation value vectors by arranging the ncorrelation values on polar coordinates at intervals of an angle of2π(n/m) radians, and adding the n correlation value vectors to calculatean angle of a resultant vector of the n correlation value vectors; andestimating a symbol timing of the received signal based on the angle ofthe resultant vector.
 5. The non-transitory computer-readable recordingmedium according to claim 4, wherein the computer program causes thecomputer to calculate the resultant vector of the n correlation valuevectors when any of the correlation values Rn exceeds a certainthreshold, the generating n correlation value vectors, the combining then correlation value vectors, and the calculating the angle.